1. Field of the Invention
The present invention relates to an implant and a surgical technique for treating neovascular glaucoma, and particularly to improvements in the anterior chamber tube shunt to an encircling band procedure.
2. Description of Prior Art
Glaucoma, a disease of the eye which may ultimately cause blindness, is caused by increased intraocular pressure. Since as early as 1906, surgical techniques have been attempted to treat glaucoma by lowering intraocular pressure. A modern surgical technique has been described by Schocket et al, in an article entitled "Anterior Chamber Tube Shunt to an Encircling Band in the Treatment of Neovascular Glaucoma", Ophthalmology, Vol. 89, No. 10, pp. 1188-1194, 1982, and in another article entitled "Anterior Chamber Tube Shunt to an Encircling Band in the Treatment of neovascular Glaucoma and other Refractory Glaucomas", Ophthalmology, Vol. 92, No. 4, pp. 553-562, 1985.
According to the teachings of the above mentioned articles, aqueous is shunted from the anterior chamber of the eye to the orbit in order to reduce the intraocular pressure. The aqueous escapes through a tube inserted into the anterior chamber which is connected to a band which encircles the circumference of the eye. The aqueous fluid is shunted to an encapsulated reservoir and then diffuses through the capsular wall into the orbit to thereby lower the intraocular pressure.
Approximately two weeks after such surgery, the implanted materials become surrounded by a fibrous capsule separating the implant from the host tissue, a capsule that is contiguous with the tissue but not adherent to the implant. The capsule is apparently an attempt to destroy or isolate what the host tissue recognizes to be a foreign body. This encapsulation is essential for success and recovery in response to the surgical procedure.
Although this above-described work was a significant advance over the art, the implant of this surgical procedure can be improved. First, the surgically treated eye could be subject to bleeding into the anterior chamber. This could potentially occur at the time of insertion of the tube into the anterior chamber or shortly thereafter. As a consequence, blood clotting could occur which could block the opening in the tube needed to transport the aqueous from the eye, cause an increase in intraocular pressure, and render the procedure ineffective. This especially could occur in patients with severe rubeosis iridis.
An additional problem that could result with the known implant is that the patient could suffer from hypotony for a time period lasting from implantation until formation of the fibrous capsule around the implanted materials. Hypotony occurs when aqueous outflow from the chamber exceeds aqueous production as seen after insertion of the implant and causes too low an intraocular pressure and a corresponding flat anterior chamber. This could lead to further pathologic problems such as cataracts, adhesions of iris to cornea or lens, and in eyes which have had prior surgery, hemorrhagic choroidal detachments with a resultant loss of vision.
Further, although encapsulation of the implant is necessary for success of the surgical procedure, limiting the thickness of the capsule wall is desirable since this allows less restrictive movement of aqueous fluid out of the encircling band into the orbit and thereby ensures a good flow of aqueous. The known procedure did not possess this desired benefit.
Others have sought to remedy these problems, most notably the hypotony problem which occurs shortly after surgical implantation.
U.S. Pat. No. 3,788,327 to Donowitz et al disclose a surgical implant device. The Donowitz et al device is designed to rest on the surface of the cornea whereby a shank-like member with a valve to control intraocular pressure is mounted through the eye into the anterior chamber. Because the device is physically mounted onto the eye itself, friction occurs between the eyelid and the device. Additionally, the escaping aqueous flows to the cornea and not to the orbit. Furthermore, the valve in the Donowitz et al device must be permanently mounted in the shank to control the pressure in the anterior chamber.
U.S. Pat. No. 4,402,681 to Haas et al disclose an artificial implant valve. This valve is disadvantageous in that it is mounted into the posterior segment of the eye, and therefore it is difficult to adjust or remove the valve in the event of surgical complications. Further, the valve must remain permanently mounted to the eye to be effective. In addition, the construction of the valve in the Haas et al patent is composed of several parts and is complex.
Krupin et al disclosed valve implants for reducing intraocular pressure in an article entitled "Valve Implants in Filtering Surgery", American Journal of Opthalmology, Vol. 81, No. 2, pp. 232-235, 1976. The Krupin et al implant consists of a supramid tube which is cemented to a silastic tube. The end of the supramid tube is beveled and surgically inserted into the anterior chamber. The silastic tube remains outside the anterior chamber and has on its surface horizontal and vertical slits which function as a unidirectional valve. The Krupin et al device poses problems in that the valve is located in the silastic tube outside the anterior chamber. Therefore, if there are problems with the device, the conjunctiva and Tenon's Capsule must be surgically re-entered. Further, the device is designed so that the valve must be permanently mounted in the device if the device is to be effective.
Molteno et al also have developed a method of treating glaucoma. See Molteno et al, "Two Stage Insertion of Glaucoma Drainage Implants", Trans. Ophthal. Soc. N.Z., Vol. 31, pp. 17-26, 1979. According to the Molteno et al technique, a silicone tube is attached to a circular plate which is sutured to the globe. A silastic tube which is connected to the plate is sutured to the the sclera but is not inserted into the anterior chamber. Eight weeks later, a second operation is performed whereby the silastic tube is inserted into the anterior chamber. The Molteno et al procedure, therefore, requires two separate surgical operations to treat neovascular glaucoma and prevent hypotony.
White has disclosed a glaucoma pump shunt in "A New Implantable Ocular Pressure Relief Device: A Preliminary Report", Glaucoma, Vol. 7, pp. 289-294, 1985. The device consists of an inlet tube, an outlet tube, and a reservoir which connects the two tubes. Valves are located in both the inlet tube and the outlet tube, each valve located near the connecting reservoir. The end of the inlet tube located opposite from the connecting reservoir is mounted into the interior chamber. The reservoir is seated on the sclera and the posterior portion of the outlet tube is positioned in the sub-Tenon's space. This device is disadvantageous because of the intricate mounting of the reservoir and outlet tube, and because the inlet tube valve is located on the sclera and not in the anterior chamber, making it difficult to repair or replace the valve in case of failure. Additionally, because of the design of this system, the inlet and outlet valves are permanently mounted to the inlet and outlet tubes for the entire period when the device is implanted. Furthermore, the device is designed so that the reservoir permanently rests on the sclera and can potentially cause friction and erosion of the sclera and the conjunctive.
The inventor, in parent U.S. Application Ser. No. 877,342, filed June 23, 1986, prevents hypotony by utilizing a valve which takes the form of a temporary restriction. The valve is constructed so that it functions during the ten day to two week critical period when hypotony is most likely to occur. Thereafter, the valve is destroyed by a procedure such as a laser procedure, or the valve itself is made of a bio-destructible material such as collagen which automatically breaks down after the critical time period. Although this is an improvement upon existing technology, the presence of the restriction presents minor problems.
The problems associated with the restriction are two-fold. First, due to the nature of the restriction, the silastic tube attached to a silicone band can become completely clogged because of its reduced cross-sectional area. Moreover, additional means are necessary to ultimately destroy the valve after hypotony is no longer a risk.
Thus, a need exists for a simplified surgical procedure to treat glaucoma which may be performed in one step where the implanted device is easily accessible is follow-up surgery is needed to correct complications. Further, a need exists to prevent hypotony shortly after the surgical device is implanted without requiring the use of flow restricting means. Additionally, a need exists to regulate the volume of aqueous flowing from the anterior chamber and to ensure that aqueous flows from the chamber to thereby prevent a buildup of intraocular pressure. Further, a need exists to prevent bleeding associated with the surgical technique and to prevent clogging of the implant caused by blood clots located in the opening or within the lumen of the tube of the implant.